Reduction of greenhouse gas emission

ABSTRACT

Herein disclosed is a method of reducing greenhouse gas (GHG) emission comprising introducing one or more feed streams into a reformer to generate synthesis gas; and converting synthesis gas to dimethyl ether (DME). In some cases, the reformer is a fluidized bed dry reforming reactor. In some cases, the reformer comprises a hydrogen membrane. In some cases, the hydrogen membrane removes hydrogen contained in the synthesis gas and shifts reforming reactions toward completion.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Patent Applications No. 62/357,521 filed Jul. 1, 2016, thedisclosure of which is hereby incorporated herein by reference in itsentirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND Field of the Invention

This disclosure relates generally to the reduction of greenhouse gas(GHG) emission. More particularly, this disclosure relates to thereduction of greenhouse gas (GHG) emission via dry reforming of naturalgas.

Background of Invention

The recent UN Climate Conference (COP 21) achieved commitments from mostcountries on specific GHG emission reductions, to limit globaltemperature rise at or below 2 degrees Celsius, by the end of thiscentury. There is general consensus among the scientific community thatthis will require a reduction in GHG emissions in the order of 50% fromcurrent levels by 2050, with complete phase out of fossil fuel derivedGHG emissions later in the century, by around 2080. This change willrequire very significant changes to the world's current energyinfrastructure.

Some of these reductions will be achieved by deployment of solar, wind,nuclear energy along with increased use of electric vehicle technologiesand a wide range of energy efficiency improvements. These morecommercially available technologies are less able to replace the currentenergy infrastructure in the transportation sector, namely for heavyvehicle and long haul aircraft.

Unfortunately, conventional gas-to-liquid (GTL) technologies, by andlarge, do not achieve significant GHG emission reductions versusconventional oil refining; and in some cases result in higher overallwheel-to-wheel GHG emissions. They also typically require very large netwater usages and often import dirty power. Hence, conventional GTLtechnologies don't appear to address the specific commitments made atCOP 21.

Hence, there is an urgent need to find an environmentally acceptablepath to transition from the current crude oil based diesel and jet fuelenergy pathways to lower GHG emitting pathways for the transportationsector. A pathway that allows for utilization of the relatively cleanand abundant natural gas resource that is available, while stillachieving targeted GHG emissions reductions would be very beneficial.The pathway would also need to consider water usage as a key metric, asmany areas of the world have water usage restrictions.

As such, there is continuing interest and need to develop suitablemethods and systems to reduce GHG emissions while providing the need offuel, e.g., in the transportation sector.

SUMMARY

Herein disclosed is a method of reducing greenhouse gas (GHG) emissioncomprising introducing one or more feed streams into a reformer togenerate synthesis gas; and converting synthesis gas to dimethyl ether(DME). In an embodiment, the reformer is a fluidized bed dry reformingreactor. In an embodiment, the reformer comprises a hydrogen membrane.In an embodiment, the membrane is coated with an erosion resistantlayer. In an embodiment, the hydrogen membrane removes hydrogencontained in the synthesis gas and shifts reforming reactions towardcompletion.

In an embodiment, reformed gas exits the top of the reformer and isseparated from spent catalyst. In an embodiment, spent catalyst isrouted to a regenerator in which the catalyst is regenerated.

In an embodiment, a renewable fuel is used in the regenerator. In anembodiment, the renewable fuel comprises landfill gas, bio-digester gas,pyrolysis oils and liquid fuels, spent glycerol, biomass derived syngas,bio-ethanol (ethanol produced from biogenic sources). In an embodiment,the regenerator comprises an air pre-heater and the process utilizesfull or partial displacement of natural gas or natural gas derivedsyngas with a bio-genic gaseous or liquid fuel in the air pre-heater. Inan embodiment, the method uses full or partial displacement of naturalgas or natural gas derived syngas with a bio-genic gaseous or liquidfuel in the regenerator. In an embodiment, the renewable fuel used inthe regenerator comprises high molecular weight cellulose degradationproducts. In an embodiment, the renewable fuel used in the regeneratorcontains impurities including arsenic, sulfur, ammonia, chlorine, orcombinations thereof.

In an embodiment, the method uses full or partial displacement ofnatural gas feedstock with a bio-genic gaseous feedstock in thereformer. In an embodiment, the one or more feed streams comprisenatural gas and renewable feedstocks. In an embodiment, the renewablefeedstocks comprise landfill gas, bio-digester gas, bio-genicfeedstocks.

In an embodiment, the reformer uses no process water and requires nooxygen. In an embodiment, the method of this disclosure produces CO2emissions of less than 180 g CO2/liter of dimethyl ether (DME). In anembodiment, the method of this disclosure produces equivalent greenhousegas emissions (GHGe) of less than 0.30 kg GHGe/mile using the standardGREET model

The foregoing has outlined rather broadly the features and technicaladvantages of the invention in order that the detailed description ofthe invention that follows may be better understood. Additional featuresand advantages of the invention will be described hereinafter that formthe subject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and the specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of theinvention. It should also be realized by those skilled in the art thatsuch equivalent constructions do not depart from the spirit and scope ofthe invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the preferred embodiments of theinvention, reference will now be made to the accompanying drawings inwhich:

FIG. 1 is a simplified block flow diagram illustrating the process forthe production of DME from natural gas, according to an embodiment ofthis disclosure.

FIG. 2 is a sketch illustrating the configuration of a reformer reactor,according to an embodiment of this disclosure.

FIG. 3 is a diagram graph illustrating the ability to produce a 1:1H₂:CO syngas at elevated pressure and reduced temperature in thereforming reactor, according to an embodiment of this disclosure.

FIG. 4 shows an experimental set up of dry reforming, according to anembodiment of this disclosure.

FIG. 5 illustrates an overall process flow sheet for processintegration, according to an embodiment of this disclosure.

DETAILED DESCRIPTION

Herein disclosed is a method of reducing greenhouse gas (GHG) emissioncomprising introducing one or more feed streams into a reformer togenerate synthesis gas; and converting synthesis gas to dimethyl ether(DME). In an embodiment, the reformer is a fluidized bed dry reformingreactor. In an embodiment, the reformer comprises a hydrogen membrane.In an embodiment, the membrane is coated with an erosion resistantlayer. In an embodiment, the hydrogen membrane removes hydrogencontained in the synthesis gas and shifts reforming reactions towardcompletion.

In an embodiment, reformed gas exits the top of the reformer and isseparated from spent catalyst. In an embodiment, spent catalyst isrouted to a regenerator in which the catalyst is regenerated.

In an embodiment, a renewable fuel is used in the regenerator. In anembodiment, the renewable fuel comprises landfill gas, bio-digester gas,pyrolysis oils and liquid fuels, spent glycerol, biomass derived syngas.In an embodiment, the regenerator comprises an air pre-heater and theprocess utilizes full or partial displacement of natural gas or naturalgas derived syngas with a bio-genic gaseous or liquid fuel in the airpre-heater. In an embodiment, the method uses full or partialdisplacement of natural gas or natural gas derived syngas with abio-genic gaseous or liquid fuel in the regenerator. In an embodiment,the renewable fuel used in the regenerator comprises high molecularweight cellulose degradation products. In an embodiment, the renewablefuel used in the regenerator contains impurities including arsenic,sulfur, ammonia, chlorine, or combinations thereof.

In an embodiment, the method uses full or partial displacement ofnatural gas feedstock with a bio-genic gaseous feedstock in thereformer. In an embodiment, the one or more feed streams comprisenatural gas and renewable feedstocks. In an embodiment, the renewablefeedstocks comprise landfill gas, bio-digester gas, bio-genicfeedstocks.

In an embodiment, the reformer uses no process water and requires nooxygen.

Dry reforming of natural gas provides some improvement in the GHGemissions for GTL plants, at least better than previously proposed bi-and tri-reforming technologies. 100% dry reforming of natural gas, usinga fluidized bed membrane reactor to make 1:1 H2:CO syngas, which is thenused to make Dimethyl Ether (DME, as discussed in further details hereinbelow) is able to achieve the goal of production of a low emissiondrop-in diesel fuel substitute with lower wheel-to-wheels GHG emissions,while using little water and no import power. In addition, DME is auseful chemical intermediate, a direct LPG substitute, an intermediatein the production of drop-in motor gasoline and a potential fuel in gasturbines and diesel generators.

The overall chemical reaction for the process of the production ofDimethyl Ether (DME) (C₂H₆O) from methane and carbon dioxide is: 3CH₄+CO₂=2 C₂H₆O.

In this process, carbon dioxide is consumed and converted into a usefulproduct DME that can be used as a transportation fuel including as areplacement for diesel.

The dry reforming step uses a fluidized bed reactor with a Ni catalystto convert methane to syngas. CH₄+CO₂=2H₂+2CO

It is generally not easy to get to a H₂ to CO ratio of 1 in the productin practice. Catalysts often coke, deactivate, or are limited in theconversion of methane and result in a lower H₂ to CO ratio than desired.

The syngas to DME reaction can be written as: 6H₂+6 CO=2 C₂H₆O (DME)+2CO₂

In some cases, the fluidized bed dry reforming reactor also contains ahydrogen membrane to preferentially remove hydrogen produced and forcethe reaction toward full conversion of the CO₂ and methane.

This dry reforming process is superior to other routes for theproduction of DME. It uses less natural gas than competing processes,uses no process water, and requires no oxygen plant, and hassignificantly lower greenhouse gas (GHG) emissions than the competingprocesses for DME production.

FIG. 1 shows a simplified block flow diagram for this process. FIG. 1also illustrates flows and balances for a commercial process for theproduction of DME from natural gas.

Dry reforming. A pressurized fluidized bed (dry) reforming reactorutilizing Pd alloy membranes, or Pd alloy membranes supported on ceramicor other metal substrates inserted into the fluidized bed for thepurpose of permeating H₂ generated in the dry reforming reaction. In anembodiment, the membranes are coated with an erosion resistant layer. Ahydrocarbon feed stream, containing carbon dioxide or co-fed with carbondioxide, is fed and distributed into the base of the fluidized bedreformer, via a manifold or distributor. The reformer vessel ispartially filled with a fluidizable nickel based catalyst, suitable fordry reforming operating conditions.

Reformed gas exits the top of the fluidized bed reformer, where it isseparated from the catalyst. Spent catalyst is routed to a regenerator,where the catalyst is regenerated in an oxidizing environment. Theregenerated catalyst is returned to the Reformer. In an embodiment,hydrogen produced in the reformer is extracted from the reformerfluidized bed, via multiple vertically oriented palladium alloysupported on porous steel tubes or ceramic substrates or other metallicsubstrates, essentially 100% selective to H₂, located within thefluidized bed. The permeated H₂ is collected from the multiple membranetubes via internal manifold(s), which route the H₂ to an externalcollection system.

As H₂ is permeated from the fluidized bed reformer, the dry reformingequilibrium is shifted such that dry reforming reactions can proceed tocompletion. The H₂ permeation facilitates the high degree of dryreforming, without the use of any steam injection into the reformer, atlower reforming temperatures and higher pressures than without the H₂membranes.

Reformer/reforming reactor/reformer reactor. In an embodiment, FIG. 2shows the configuration of the reformer reactor. The reformer operatesat approximately 600-700° C. at a pressure of 700-800 kPa. Catalyst isfluidized by the incoming methane (or other hydrocarbon) and carbondioxide feed. The feed gas passes through a gas distributor. Thecatalyst-gas mixture is in a fluidized bed. Inside the fluidized bed thehydrogen membranes tubes are placed hanging from the top of thereformer. The methane and carbon dioxide are reacted over the fluidizedcatalyst. The reaction will cause the formation of hydrogen and carbonmonoxide via the dry reforming reaction.

In an embodiment, hydrogen will permeate through the membranes and becollected as hydrogen product leaving the reactor. The methane andcarbon dioxide will continue to react as some of the hydrogen permeatesaway producing more hydrogen and carbon monoxide.

In some embodiments, the reformer has a top section that contains acyclone for solid gas separation. Some amount of catalyst will continueto be transported toward the top of the reactor. The gas/catalystmixture will enter the cyclone and the solid catalyst particles willseparate from the gas and fall back toward the bottom of the reactor.The gas produced leaves the top of the reformer. Catalyst also leavesvia side withdrawal near the bottom of the reactor through an exit andthe catalyst will then proceed to the regenerator. Regenerated catalystenters the reformer catalyst bed as hot catalyst that supplies heat tothe reformer. The catalyst will enter at approximately 900-1000° C. Thecatalyst residence time in the reformer is in the range of 0.5-4minutes. The fluidized bed is preferentially operated in turbulentregime. The gas superficial velocity is in the range of 1-3 m/s.

Hydrogen Membranes. The addition of the hydrogen membranes to thereformer is optional but preferred. H₂ produced in the reformer isextracted from the reformer fluidized bed, via multiple verticallyoriented palladium alloy supported on a porous ceramic substrate,essentially 100% selective to H₂, located within the fluidized bed. Thepermeated H₂ is collected from the multiple membrane tubes via internalmanifold(s), which route the H₂ to an external collection system.

As H₂ is permeated from the fluidized bed reformer (the fuel reactor),the dry reforming equilibria is shifted such that dry reformingreactions can proceed more or less to completion. The H₂ permeationfacilitates a higher degree of dry reforming, without the use of anysteam injection into the reformer, at lower reforming temperatures andhigher pressures than without the H₂ membranes. FIG. 3 is a diagramillustrating the ability to produce a 1:1 H₂:CO syngas at elevatedpressure and reduced temperature in the reforming reactor. FIG. 4 showsan experimental set up of dry reforming.

Metallic membranes or metal coated ceramic supported membranes are hunginside the dual fluidized bed reactor, such as Pd or Pd alloy coatedcylindrical structures hung inside the fluidized bed reactor or anyother suitable structures. Palladium (Pd) based membranes have highhydrogen permeability and an almost infinite selectivity to hydrogen. Athin coating of Pd or Pd alloy 2-50 microns thick (with the minimalthickness being preferred for permeation but slightly thicker membranesdesired for long term stability of the membrane) is deposited on thecylindrical support material. Ag, Pt, Au, Rh, Ru, and Pb additives havebeen added to the Pd to form alloys and improve hydrogen permeability.Self-supporting tubular hydrogen membranes have been successfully scaledup and are also contemplated for use in this catalytic membranereactor/reformer.

The permeation rate through the hydrogen membranes varies significantly.The hydrogen permeation flux rates can vary from 10-300 NM3 H2/hr/m2 ofmembrane area with the preferred range of 20-80 NM3 H2/hr/m2. Thepermeate pressure is relatively low at sub-atmospheric pressure (as lowas 1 psia or approximately 7 kPa). The proper choice of the balancebetween membrane surface area, hydrogen permeation, and overall reactorperformance dictate the exact configuration of the reactor/reformersystem.

The hydrogen product that goes to the manifold is then compressed andblended back with the reformer product gas to produce a combined syngaswith a 1:1 hydrogen to carbon monoxide ratio. In some cases, sweep gason the permeate side of the membrane is used to increase the flux at ahigher pressure and reduce compression costs. If sweep gas is needed ordesired, syngas or reformer product gas can be used as the sweep gas aswell as steam.

The Nickel catalyst in the reformer with a mean particle size ofapproximately 200 microns and a nickel content of 2-6 wt % on an alphaalumina support. For use in the system, the catalyst must befluidizable, generically spherical, and must be attrition resistantduring operation. Suitable nickel alumina catalyst is disclosed, forexample, in international patent application number PCT/US2005/036588,which is hereby incorporated herein in its entirety for all purposes notcontrary to this disclosure and suitable nickel catalyst is disclosed,for example, in U.S. Pat. No. 7,915,196 hereby incorporated herein inits entirety for all purposes not contrary to this disclosure.

Regenerator. Catalyst from the reformer is sent to the regenerator. Thecatalyst in the reformer can become deactivated by contaminants or bycarbon deposited on the catalyst during the dry reforming reaction.Carbon formation during dry reforming reaction is one of the commonproblems with dry reforming process that uses a fixed bed. One of theadvantages of using a fluidized bed reactor is that the catalyst can beregenerated frequently in air.

In an embodiment, the regenerator operates at approximately 700-1000° C.and catalyst is fluidized by air supplied by an air blower or othermeans at the bottom of the regenerator. Any carbon on the catalyst isburned off in the regenerator. In one embodiment, the regenerator is afast fluidized bed where the air and catalyst are mixed at the bottom ofthe regenerator and the catalyst is conveyed to the top of theregenerator where the catalyst and flue gas are separated out. Thesuperficial gas velocity in the regenerator dense bed is maintained at1-3 m/s. The hot catalyst then recirculates to the entry nozzle on thereformer. In some embodiments, there is very little or no excess oxygenat the top of the regenerator.

In cases wherein carbon on the catalyst is not sufficient to keep theregenerator at the high temperature needed, supplemental fuel can beburned in the regenerator to heat the regenerator to operatingtemperature. In one embodiment, a mixer/burner is placed in theregenerator or adjacent to the regenerator vessel. Fuel and air aremixed and burned in the burner with the combustion product gases flowinginto the regenerator and supplying any needed heat to the system. In anembodiment, methane is used as the supplemental fuel to the regenerator.In other embodiments, other fuels to the regenerator are used, such asrenewable fuels including landfill gas, bio-ethanol, bio-digester gas,pyrolysis oils and liquid fuels, spent glycerol, biomass derived syngas.Alternatively, biomass is used in a biomass boiler where the hot fluegas from the boiler is used to heat the regenerator to operatingtemperature.

DME Production from Syngas. The hydrogen from the manifold is compressedand blended with the reformer product gas to produce a 1:1 H2/CO ratiosyngas. The blended syngas is compressed to approximately 5500 kPa. Theblended syngas is reacted to produce primarily a Dimethyl Ether productby this reaction: 6H₂+6 CO=2 C₂H₆O (DME)+2 CO₂

In various embodiments, a single step is used to convert syngas to DME.There are multiple-step reactions that can also obtain DME as a productincluding a first step where syngas is converted to methanol and thenmethanol is dehydrated to DME. For one step synthesis, a bifunctionalcatalyst is used that does methanol synthesis and dehydration. There area number of catalysts that can produce DME, such as mixtures of methanolcatalyst (CuO/ZnO/Al2O3) with methanol dehydration catalysts(gamma-alumina). Other bifunctional catalysts such as Ni/Ce-ZrO2/Al2O3,CuO—ZnO—Al2O3 (CZA) over Clinoptilolite, CZA over various zeolitesincluding ferrierite, ZrO2, ZSM-5, NaY or HY, are also used.

In an embodiment, slurry reactors and fixed bed reactors are used toproduce DME from syngas. In an embodiment, a multi-tubular fixed bedreactor is used to produce DME from syngas to take advantage of theexothermic DME reaction and to better control reactor temperature andavoid hot spots.

In an embodiment, the conversion reactor has individual tubes of 20-30mm in diameter filled with catalyst pellets. Syngas passes through thetubes and react to produce DME. In some embodiments, the reactor tubesare placed inside a shell. In some cases, inside the shell and aroundthe tubes, water is circulated to regulate reactor temperature. Throughthe heat release in the reactor tubes, steam is generated in the shell.

In further embodiments, DME product is recovered from the outlet of themulti-tubular reactor and separated as product. CO₂ byproduct, producedin the DME synthesis loop, is separated for recycle to the dry reformer,via conventional distillation. The additional CO₂ required to satisfythe dry reforming stoichiometry is recovered from the pressurizedregenerator flue gas, using an amine unit with a solvent such asmethyldiethanolamine (MDEA). The CO₂ is then recycled as feed to the dryreforming reactor.

Process integration. In an embodiment as shown in FIG. 5, the process asdescribed herein is integrated for commercial application. Thecomponents in FIG. 5 are explained in Table 1. Other alternative andequivalent arrangements are also possible, which are considered to bewithin the scope of this disclosure.

TABLE 1 10 Fluidizing nitrogen 12 Hydrogen 14 Natural gas feedstock 16External fluegas 18 Natural gas knockout drum 20 Hydrodesulfurizerfeed/effluent exchanger 22 Hydrodesulfurizer feed preheater 28Hydrodesulfurizer vessel 30 CO2 plus loop purge 32 Natural gas fuel 34Natural gas plus CO2 feed 36 Reformer 38 Recycle gas 40 Hydrogen 42Hydrogen compressor 42 Reactor effluent 44 Recycle compressor 46Synthesis gas knockout drum 48 Process condensate 50 Air compressor 52Synthesis gas compressor 54 Synthesis gas 56 Converter (DME Reactor) 58Converter Steam Drum 60 Circulator 62 Hydrogen permeate 64 Fuelgas 66Loop Purge Recycle 68 Dimethyl ether (DME) 70 DME Column 72 CO2 Column74 CO2 Compressor 76 Expander 78 Methanol Column 80 Methanol 82 Fuseloil 88 Wastewater 90 Amine Regenerator 92 Amine Pump 94 CO2 Absorber 96Fluegas Compressor

TABLE 2 Alternate Proposed Tri- Dry Reforming Alternate Tri- ReformingScheme Reforming Parameter Units Scheme (KOGAS) Scheme (JFE) Natural GasMJ (LHV)/liter 25-27 26.9 27.6 Consumption DME (incl. fuel) ProcessWater Liter H2O/liter 0 0.65 0.6 Consumption DME Oxygen Kg/liter DME 00.69 0.67 Consumption GHG emissions G CO2/liter 120-172 267 272 DME

Advantages. The process as described herein has many advantages overexisting processes for the production of DME. This process has (1) lowernatural gas consumption per liter of DME produced, (2) no process waterconsumption, (3) no oxygen consumption, and (4) lower greenhouse gas(GHG) emissions per liter of DME produced. In an embodiment, the methodof this disclosure produces CO2 emissions of less than 180 g CO2/literof dimethyl ether (DME). In an embodiment, the method of this disclosureproduces equivalent greenhouse gas emissions (GHGe) of less than 0.30 kgGHGe/mile. The details of these advantages are shown in Table 2 as thisprocess is compared with tri-reforming schemes.

This process also has the flexibility to achieve additional GHG emissionreductions, as may be required by mandated new emission standards or asincentivized by new policy (e.g. carbon cap and trade, etc). Thisflexibility is provided by:

-   -   Ability to utilize a renewable fuel in the catalyst regenerator.        These renewable fuels include landfill gas, bio-digester gas,        pyrolysis oils and liquid fuels, spent glycerol, biomass derived        syngas, etc.    -   Ability to co-feed natural gas and renewable feedstocks to the        reformer, to generate syngas for downstream DME synthesis. These        co-feeds include landfill gas, bio-digester gas or other        relatively clean bio-genic feedstocks.

Hence, the process as discussed herein provides a technology pathwayable to replace, over time, some of the existing oil refining andchemicals production infrastructure, and achieve reduced wheel-to-wheelsGHG emissions and water usage. For example, this method may be deployedinitially using 100% fossil based feedstock and fuel, but has theflexibility to transition to 0-100% renewable fuel and feedstock in thefuture, without changes to the core process. In this regard, thisprocess is part of the solution to meeting GHG emission reductiontargets, particularly for jet and diesel fuel requirements for heavyvehicles and long haul aircraft as well as for several importantindustrial chemicals.

In an embodiment, stricter GHG emission targets are complied with anddisplacement of some natural gas fuel or feedstock are achieved, aslower cost bio-genic materials are readily available, by full or partialdisplacement of natural gas, in a progressive manner. The envisagedsteps comprise:

(1) Full or partial displacement of natural gas or natural gas derivedsyngas with a bio-genic gaseous or liquid fuel in the directly firedregenerator air pre-heater.

(2) Full or partial displacement of natural gas or natural gas derivedsyngas with a bio-genic gaseous or liquid fuel in the Regeneratorfluidized bed.

(3) Full or partial displacement of natural gas feedstock with abio-genic gaseous feedstock in the dry reformer.

This progression allows for the maximum utilization of currentlyabundant, cheap and clean natural gas resources, and ensures that theimpact of potential impurities in the bio-genic fuels and feedstocks ismanaged successfully. Potential impurities in some of the bio-genicfuels and feedstocks include sulfur, alkalis, chlorides, other ashconstituents, heavy metals in addition to high molecular weightbyproducts from cellulose degradation. In various embodiments, bio-genicfuels and feedstocks with higher levels of specific impurities areutilized more successfully in the oxidizing environment in theregenerator air preheater or in the regenerator fluidized bed. Invarious embodiments, bio-genic materials, with lower levels of specificimpurities, are suitable for use as a feedstock in the dry reformer.

In an embodiment, high molecular weight cellulose degradation products,as would be expected in pyrolysis oils generated from fast pyrolysis ofbiomass feedstocks, is readily introduced into the regenerator fluidizedbed, where they are combusted to produce CO₂ instead of resulting incarbon laydown on the catalyst (if they are introduced directly into thedry reformer, which can adversely impact the catalyst activity, if thecatalyst is not properly regenerated).

Impurities such as arsenic (as As or AsH3) is a potential poison forreforming catalysts and is volatile and reactive in high temperaturereducing environments and is likely to absorb on catalyst surfaces inthe dry reformer. The oxidized forms of arsenic are less problematic, ifthese impurities are introduced directly into the regenerator.

Sulfur is a poison for the Palladium membrane in the dry reformer(although Pd alloys in some cases are made with a certain level ofsulfur tolerance). In various embodiments, fuels with significantresidual sulfur content is routed to the regenerator, wherestoichiometric removal of the sulfur, as SO₂ in the flue gas, isexpected. This is also beneficial with regards to overall nickelcatalyst activity.

Other impurities such as ammonia and chlorine may also adversely effectthe Pd membrane in the dry reformer. In embodiments, fuels high innitrogen or in chlorine, is routed to the regenerator. This is alsobeneficial with regards to nickel catalyst activity maintenance.

As stated earlier, conventional GTL technologies produce wheel-to-wheelGHG emissions that are often worse than conventional refined dieselpathways. Some preliminary GREET analysis indicates the followingWheel-to-wheel GHG emissions:

Conventional ULSD: 0.345 kg GHG_(e)/mile traveled.

Conventional GTL (DME): 0.357 kg GHG_(e)/mile

Dry Reforming Nat Gas (DME): 0.333 kg GHG_(e)/mile

Dry Reforming (DME) w/bio-genic fuel source: 0.237 kg GHG_(e)/mile

DR (DME) w/bio-genic fuel+50% feedstock: 0.177 kg GHG_(e)/mile

While preferred embodiments of the invention have been shown anddescribed, modifications thereof can be made by one skilled in the artwithout departing from the spirit and teachings of the invention. Theembodiments described herein are exemplary only, and are not intended tobe limiting. Many variations and modifications of the inventiondisclosed herein are possible and are within the scope of the invention.Where numerical ranges or limitations are expressly stated, such expressranges or limitations should be understood to include iterative rangesor limitations of like magnitude falling within the expressly statedranges or limitations (e.g., from about 1 to about 10 includes, 2, 3, 4,etc.; greater than 0.10 includes 0.11, 0.12, 0.13, and so forth). Use ofthe term “optionally” with respect to any element of a claim is intendedto mean that the subject element is required, or alternatively, is notrequired. Both alternatives are intended to be within the scope of theclaim. Use of broader terms such as comprises, includes, having, etc.should be understood to provide support for narrower terms such asconsisting of, consisting essentially of, comprised substantially of,and the like.

Accordingly, the scope of protection is not limited by the descriptionset out above but is only limited by the claims which follow, that scopeincluding all equivalents of the subject matter of the claims. Each andevery claim is incorporated into the specification as an embodiment ofthe present invention. Thus, the claims are a further description andare an addition to the preferred embodiments of the present invention.The disclosures of all patents, patent applications, and publicationscited herein are hereby incorporated by reference, to the extent theyprovide exemplary, procedural or other details supplementary to thoseset forth herein.

What is claimed is:
 1. A method of reducing greenhouse gas (GHG)emission comprising introducing one or more feed streams into a reformerto generate synthesis gas; and converting synthesis gas to dimethylether (DME).
 2. The method of claim 1 wherein said reformer is afluidized bed dry reforming reactor.
 3. The method of claim 1 whereinthe reformer comprises a hydrogen membrane or a hydrogen membrane coatedwith an erosion resistant layer.
 4. The method of claim 3 wherein saidhydrogen membrane removes hydrogen contained in the synthesis gas andshifts reforming reactions toward completion.
 5. The method of claim 1wherein reformed gas exits the top of the reformer and is separated fromspent catalyst.
 6. The method of claim 5 wherein spent catalyst isrouted to a regenerator in which the catalyst is regenerated.
 7. Themethod of claim 6 wherein a renewable fuel is used in the regenerator.8. The method of claim 7 wherein the renewable fuel comprises landfillgas, bio-digester gas, pyrolysis oils and liquid fuels, spent glycerol,biomass derived syngas, bio-ethanol.
 9. The method of claim 7 whereinthe regenerator comprises an air pre-heater and the method utilizes fullor partial displacement of natural gas or natural gas derived syngaswith a bio-genic gaseous or liquid fuel in the air pre-heater.
 10. Themethod of claim 7 comprising using full or partial displacement ofnatural gas or natural gas derived syngas with a bio-genic gaseous orliquid fuel in the regenerator.
 11. The method of claim 7 wherein therenewable fuel used in the regenerator comprises high molecular weightcellulose degradation products.
 12. The method of claim 7 wherein therenewable fuel used in the regenerator contains impurities includingarsenic, sulfur, ammonia, chlorine, or combinations thereof.
 13. Themethod of claim 1 comprising using full or partial displacement ofnatural gas feedstock with a bio-genic gaseous feedstock in thereformer.
 14. The method of claim 1 wherein said one or more feedstreams comprise natural gas and renewable feedstocks.
 15. The method ofclaim 14 wherein said renewable feedstocks comprise landfill gas,bio-digester gas, bio-genic feedstocks.
 16. The method of claim 1wherein said reformer uses no process water and requires no oxygen. 17.The method of claim 1 producing CO2 emissions of less than 180 gCO2/liter of dimethyl ether (DME).
 18. The method of claim 1 producingequivalent greenhouse gas emissions (GHGe) of less than 0.30 kgGHGe/mile.